A discovery system is a bibliographic search system based on search engine technology. It is part of the concept of Library 2.0 and is intended to supplement or even replace the existing OPACcatalogs. These systems emerged in the late 2000's in response to user desire for a more convenient search option similar to that of internet search engine.[1]

Large search space: A search can search the data from different data sources (the discovery system has a comprehensive central subject index). For example, you can search a journal article or a textbook directly in the discovery system and you do not have to change from a subject database to the library catalog.

Intuitive usability, like a search engine. The search is basically only a simple form, an advanced search function is not always provided.

Ranking of the results according to relevance: The "best" hit is displayed first, not necessarily the newest one. A good ranking is important because many hits are often found due to the large search space.

Search refinement with drill-down menus (facets): For example, a search can be restricted to all matches available online.

Exploratory search: One finds results of interest that were not specifically requested. For example, links to similar hits, entries in subject databases, or Wikipedia articles are displayed (integration of other web technologies).